The present invention relates to the combing and selection operations which are carried out on textile fibres prior to the spinning operation. The main purpose of combing is to remove from the material, which is generally fed along in the form of a continuous band or web, any impurities, such as dust, and also to remove any very short fibres which may be present.
In the case of organic or natural materials the fibres are usually all of different lengths and the fineness of the fibres is inversely proportional to their length.
Since the commercial value of natural textile fibres depends on, among other things, their length and fineness, it is important to be able to determine these for a given material; the composition of a material is sometimes illustrated by a diagram of the fibres which represents the percentage composition of the material as a function of the length of the fibres.
Such a diagram may be produced manually, or with the use of suitable instruments. Known instruments for this purpose operate by sifting a limited sample of the material under examination; such instruments are not, however, suitable for effecting selection of the fibres for the production of a large quantity of yarn.
In the industrial production of threads on the other hand, it is desirable to be able continuously to select fibres according to their length so that fibres of different lengths can be used for different processes, each process being the most appropriate for fibres of a given length, or relatively narrow range of lengths.
At one time, the operation of selecting the fibres on an industrial scale was effected manually and was completely independent of the actual combing operation. In modern spinning installations a manual selection operation is no longer possible partly due to the considerable complexity of the operation but mostly because of the high economic cost of manual selection. Moreover it has not yet been found possible economically to effect such a selection automatically by machine in such a manner as to collect the fibres within sufficiently narrow ranges of length.